In the mobile terminals such as mobile phones, the operation buttons mounted on, for example, a mobile phone are used for registering address information, writing address information in an address book, or inputting sentences of e-mail. Since the number of buttons which can be used as character input keys in a mobile phone is limited, a plurality of characters are assigned to each character input key. Each of the characters assigned to a character input key can be identified by the total number of times the character input key is pressed down. That is, when a character input key is pressed down once or a plurality of times, a character corresponding to the total number of times the character input key is pressed down is inputted. For example, the character “A” can be inputted by pressing down the character input key “2” once, the character “B” can be inputted by pressing down the character input key “2” twice, and the character “C” can be inputted by pressing down the character input key “2” three times.
In addition, the mobile phones make a predictive search of a dictionary database for conversion candidates each containing one or more already inputted characters, and display a result of the search on a screen. Since one of the displayed conversion candidates can be selected by using a select key, efficient operability is achieved. At this time, the mobile phones preferentially display on the screen a word or a series of words which has been previously inputted and confirmed. Specifically, the mobile phones display the words or series of words registered in the dictionary database in order of frequency of previous use, where the dictionary database is installed in the mobile phones. Thus, the total number of times the character input keys are pressed down is reduced, so that the user of each mobile phone can input characters by less operation.
In the above circumstances, a mobile phone in which the operability in character input can be improved is known (Japanese Laid-open Patent Publication No. 2007-293924).
In the above mobile phone, when a character input key in the above mobile phone is pressed down, a dictionary search unit in the mobile phone produces base character strings by combining all characters which can be inputted by the character input key and a string of unconfirmed characters which are already inputted, and searches, by reference to a dictionary, for one or more character strings each of which includes the same pronunciation as one of the base character strings. Thereafter, the mobile phone obtains one or more predicted character strings on the basis of the corresponding character string as an index, and a predicted-candidate display control unit displays the one or more predicted character strings on a screen of an output device. Then, the mobile phone overwrites the inputted character string with one of the predicted character strings which is selected by a user, and completes the display of the predicted character strings. Thus, in the above mobile phone, it is possible to reduce the number of operations of pressing down keys before obtaining desired characters, and improve the operability.
However, in the above mobile phone, a case is assumed that words or series of words registered in a dictionary database are displayed on the screen in order of frequency of use, and a word or a series of words which is displayed at a relatively low ordinal position is selected among the words or series of words displayed on the screen. In the case, the total number of operations of pressing down one or more keys is reduced and the operation is more efficient when a word or a series of words is selected by use of a character input key, than when a word or a series of words is selected by use of a select key. That is, the efficiency of the key operation (i.e., which is more efficient, to press down a character input key in preference to a select key or to press down a select key in preference to a character input key) differs according to the word or series of words to be inputted.